At a certain age, many kids try to bend the truth in their own way, and many times it is to avoid getting in trouble for something that happened unintentionally. I searched for a solution to teach them that lying is bad and came across a simple, but elegant way to get the point across clearly in their minds.
Preparation:
Ther overall idea is to bring out some icecream (or some other treat that they enjoy) with 3 separate bowls.
Add salt and a bit water to one of the bowls to that it dries and sticks to it
Add some salt into the bowl and let it dry so that it sticks to the bottom of the bowl. You may want to heat it up a bit as well.
Now call them all over for some ice cream and give them all spoons! But don't give them any yet!
Lesson 1 - Covering up a lie
Pretend to accidentally sprinkle some salt on the icecream in front of them, and then cover it up with chocolate syrup. Ask them if they still want to eat it, and you'll be surprised to how many still do! Explain that there are times when we do not do the right thing, and don't want to get in trouble so we cover it up with a lie (chocolate syrup in our case). Even though we try to cover up a lie the bad taste doesn't go away. So it's better just to tell the truth in the first place and get salt-less icecream!
Lesson 2 - Compounded lies
Next, tell them that even if they accidentally tell a lie they can go back and correct it right away. Give them a bowl with non-dried salt and have them wipe away the salt with a damp paper towel to see how easy it is to tell the truth.
Next, explain that sometimes when they tell lies, they have to cover it up with more and more lies and it gets harder and harder to remember what was said. Give them the bowl with dried salt to see how difficult it is to fix so many lies stacked on top of one another.
Lesson 3 - Tell the truth
Finally, you can clarify that each lie they tell is like a pinch of salt, and that if they want something good (such as ice-cream) they would need to eat through all that nasty salt everytime. Isn't it so much easier just to tell the truth!